About Limestone: History, Composition and Uses
Limestone is a sedimentary rock which is formed at the bottom of the ocean. It consists wholly or mainly of calcium carbonate. This calcite is sourced primarily from the shells and bones of marine organisms. The sediment that builds up preserves these organisms into fossils. Over millions of years the heat and pressure cause a chemical reaction which turns this sediment into limestone.
Visually limestone can vary considerably depending on how much calcite is present in the stone, the level of impurities and the distribution of fossils. High calcite limestone will have a very light colour while impurities such as iron oxide give it a yellow or tan appearance and the presence of carbon will darken it to a black or grey.
Limestone has a hardness rating of 3 – 4 on Moh’s scale. It is usually identified by it’s beautiful display of fossils however these are not always visibly present. Limestone which has been incorrectly maintained can sometimes show swirls of soil which can look like a natural feature of the stone. It will usually appear honed rather than polished and can be extremely porous however this can also vary greatly from one limestone to another.
- Limestone is becoming very popular among architects and interior designers as an alternative to wood or resilient floors.
- The manufacture of cement and mortar
- Portland limestone was used to build the National Gallery in London
- Building Stone: Egyptian pyramids and many early 19th century train station and banks
Restoration and Maintenance:
It is important to understand the stone maintenance cycle in order to properly maintain the beauty and lustre of your natural stone installation.
Limestone can be difficult to maintain if a proper maintenance cycle is not put in place from the point of installation. As it is usually not polished, the problem of scratching is not as big an issue as it is with marble, however, if proper barrier matting is not introduced even a honed surface will lose its attractiveness. The most important factor to consider with the maintenance of limestone is the possibility of staining. Its calcite composition makes it susceptible to acid attack from spilt food and drink. Its high porosity can also mean oil will permeate the surface and leave staining if it is not properly sealed with a penetrative sealer.
Any stone needs a well planned maintenance schedule in place to preserve it and to delay restoration procedures for as long as possible.
Daily maintenance will consist of dry dust mopping using a clean rayon mop. Regular damp mopping will also be required. This must be carried out using a good quality stone soap alternated with just freshwater. It is important that soap residue doesn’t build up on the surface of the stone. Spills should be wiped promptly to prevent staining or etching. Acid-based chemicals used for household cleaning can damage the surface of limestone and other calcite stones on contact. Similar damage from acid-based foods and beverages can be avoided if not left to dwell.
Professional regular maintenance will be required to maintain its honed or polished appearance. Our opinion is that limestone looks best with a honed or low/medium sheen appearance however many people insist on a high shine finish. Some low calcite limestone can be extremely difficult to polish and therefore vitrification would be required. Vitrification, however, is only a short term solution and can give the stone an unnatural plastic appearance if repeated too often.
When regular maintenance procedures are no longer adequate, complete restoration will be necessary. Problems like cracked, loose or chipped tiles, deep staining and incorrect maintenance causing yellowing require intensive restoration. It is common to see limestone which is very yellow and with dark swirls present due to bad maintenance. Lazy dry mopping and the use of low-quality maintenance polishes which contain high levels of wax, resulting in a stone that becomes yellow over time. The use of procedures such as vitrification or polishing at this point will only serve to trap in the dirt resulting in a shiny but soiled yellow floor. Some of our clients are sometimes surprised to see how light the original limestone is when this top layer of discoloured and over-vitrified stone is removed. With the use of diamond grinding, its true beauty can again be exposed often showing more fossils and a more diverse range of colour. The use of coloured epoxy resins will serve to repair damaged and loose tiles. Stains are removed using a poultice and deep alkaline cleaning prior to grinding and honing.
Our extensive experience in limestone restoration will give you peace of mind when choosing a stone care professional. We offer a consultancy service to architects and interior designers and our reputation in the industry is unrivaled. Please see our testimonials page and feel free to contact us for free expert advice and a no-obligation survey.